This disclosure relates generally to orifice fittings for measuring fluid flow rates through pipes or other conduits. More particularly, the disclosure relates to an orifice plate carrier for use in orifice fittings.
Fluid flow rate is the quantification of bulk fluid or gas movement, typically measured as volumetric and mass flow rates. The ability to measure reliably and accurately fluid flow rates serves an important function in a variety of processes and industries (e.g, chemical processing, oil and gas transport and production, etc.). An orifice fitting is one of many devices that may be used to measure volumetric or mass flow rate of fluids flowing through a pipe or conduit. An orifice fitting typically employs a flat, thin plate having a central orifice that is smaller in diameter than the diameter of the conduit in which the plate is disposed. The orifice plate is positioned between a sealing ring and a compression ring that may be held together by a fastener to form an orifice plate assembly. The orifice plate assembly is disposed within a plate carrier, which is, in turn, supported and aligned within the orifice fitting. The mass fluid flow rate through the conduit is calculated from the pressure differential measured across the orifice plate, as well as other parameters.
When using an orifice fitting to measure fluid flow, many factors must be considered in order to obtain accurate flow estimates. Conventionally, the orifice plate assembly is positioned within the orifice fitting with the seal and compression rings positioned on the upstream and downstream sides, respectively, of the orifice plate. A seal is provided between the seal ring and orifice plate, but no seal is provided between the orifice plate and the compression ring. With these unidirectional orifice plate assemblies, leakage may occur if the compression ring side of the orifice plate assembly is inadvertently positioned upstream. Leakage results in reduced pressure drop across the orifice plate and inaccurate estimations of fluid flow through the fitting. Thus, the orientation of the orifice plate assembly relative to the orifice plate carrier is an important consideration.
An effective seal between the orifice plate assembly and the orifice plate carrier is another important consideration. In the event that the seal between the orifice plate assembly and the orifice plate carrier distorts, even over a small region, the orifice plate assembly may rotate relative to the plate carrier and leakage may occur.
Alignment of the orifice plate carrier relative to the orifice fitting is yet another important consideration. When the plate carrier is mismounted or improperly seated within the fitting, the orifice plate may not be normal to fluid flow through the fitting or concentric within the flowbore of the fitting. Misalignment of the orifice plate causes erroneous pressure drop readings across the orifice plate and therefore, inaccurate estimates of fluid flow through the fitting.
Lastly, during insertion and extraction of the orifice plate carrier from the orifice fitting, the plate carrier may momentarily interrupt fluid flow through the orifice plate. Interruption of flow through the orifice plate causes a spike in fluid pressure upstream of the orifice plate. A sensor positioned upstream of the orifice plate then may be exposed to a fluid pressure beyond its operational limit, resulting in erroneous upstream pressure measurement.
Thus, features for an orifice plate carrier that reduce leakage around an orifice plate disposed within the plate carrier and promote concentric alignment of the orifice plate are desirable.